The invention, and method of its use, estimates the distance between an observer and an observed object through parallax. Parallax is the apparent “shift” or “movement” of an object caused by a change in the position of the observer. The use of parallax to measure distances is well established, such as the use of parallax to measure the distance between the Earth and heavenly bodies, including distant stars.
Parallax is also the basis for depth perception in human sight. Each eye “sees” a slightly different image; the fusion of these two stereo images provides the observer the ability to discern the depth of observed objects in the fused image. This aspect of the parallax effect has been used in devices to create a “three-dimensional” effect through the simultaneous viewing of a pair of stereo images. Common examples of devices that embody this use of parallax include nineteenth century stereoscopes and the ViewMaster™ toy produced by Mattel, Inc.